Method of refining molten zinciferous lead



March 26, 1935. WEFELSCHEID 1,995,593

METHOD OF REFINING MOLTEN ZINCIFEROUS LEAD Filed April 26, 1934 /nvemar;PA UL WEFE LSCH 51,0

- Attorney Patented Mar. 26, 1935 UNITED STATES METHOD OF REFININGZINCIFEROUS LEAD Paul Wefelscheid, Braubach, Germany, assignor toAmerican Lurgi Corporation,

New York,

. N. Y., a corporation of New York Application April 26, 1934, SerialN0. 722,462 In Germany May 2, 1933 18 Claims.

The present invention relates to a process of refining lead and moreparticularly to an improved method of dezincing molten lead withchlorine gas and to an improved apparatus therefor.

It is well known that heretofore various methods have been proposed fortreating zinciferous lead in a molten state with gaseous chlorine toremove its zinc content as zinc chloride. In general, dezincing wascarried out by bubbling chlorine through a bath of molten lead .or bypassing the lead through an atmosphere of chlorine'and by collecting thezinc chloride formed by reaction from the surface of the refined lead.Thus, for instance, a stream of lead was circulated froman open kettlecontaining the impure lead to a separate reaction chamber into whichchlorine gas was also being fed. The lead and the molten zinc chlorideformed by reaction were then returned directly to the open kettlethrough a pipe at the bottom of the reaction chamber which extended to apoint below the surface of the lead bath. Due to its lower specificgravity the zinc chloride slowly rose to the surface of the lead bathand formed a solid crust which was removed by skimming. The aforesaidmethod, however, presented the disadvantage that a considerable amountof manual labor and loss of time were required to remove the zincchloride dross, and that it was almost impossible to skim the surface ofthe refined zinc chloride.

molten lead clean of The final slag formed was es- 'pecially hard toremove because it was thinner and remained liquid much longer than thepre-' viously formed slag, and as it was too thin for ladeling,considerable time was lost in waiting for the lead bath to cool down toa sufiicientlylow temperature at which the slag froze so that it couldbe collected by skimming. It was also found in connection with theaforesaid method that the hot zinc chloride floating on top of themolten lead reacted with the air to which it was exposed to form zincoxychloride which, even when present ins'mall amount, was verydetrimental in the production of satisfactory zinc chloride product forthe market. Another objectionable feature was due to the loss of noxiouschlorine fumes which occurred through volatilization of the hot zincchloride and that the loss of chlorine'could only be reduced by reduc;ing the speed of the dezincing reaction. Thus, in order to prevent theescape of chlorine gas through the discharge pipe at the bottom of thereaction chamber, it was necessary to maintain the hydrostatic level ofthe lead above the pipe by operating the reaction chamber under apartial vacuum, which was caused by supplying the chlorine gas at a rateslower than the rate-of the reaction between the chlorine and the zinc.Be- .sides reducing the dezincing speed of the lead, the vacuum alsonecessitated a perfect air-tight reaction chamber to prevent the airfrom seeping into the chamber with the subsequent formation of zincoxychlorlde. It was also found necessary to keep the molten pool of leadat a temperature sufficiently low to allow the zinc chloride to freezein order to form a. solid crust or seal over the open surface of themolten lead, meant to prevent losses of chlorine in the form of volatilezinc chloride, which in an open kettle and with stirring was noticeableat about 750 F. However, the reaction between the chlorine and the zincwas exothermic and since the lead'and the products of reaction werereturned directly from the reaction chamber to the lead bath, the

temperature of the lead bath could be controlled only by retarding therate of the dezincing reaction.

Although many attempts have been made to remedy the foregoingshortcomings, the proposals, as far as I am aware, only providedproceduras wherein the rate of dezincing was reduced and none provided asolution which was wholly satisfactory and which was very efficient.

I have discovered a procedure which eliminates the aforesaidshortcomings and which is very efilcient and which provides improved andunexpected results. 1

It is an object of the present invention to provide an improved methodof dezincing lead with chlorinegas which involves the removal of zincfrom zinciferous molten lead, the continuous separation of the resultingzinc chloride from the treated lead and the returning of the treated 40lead to the main lead bath in a practically automatic and continuousmanner which is substantially free from manual labor. 7

It is a further'object of the invention to provide a process by means ofwhich the refined lead with the reaction chamber to effect theseparation of the zinc chloride from the treated lead.

Other objects and advantages of the invention will be apparent from thefollowing description taken in conjunction with the accompanying drawingwhich illustrates in a diagrammatic manner a preferred embodiment of anapparatus for carrying the present process into practice;

In the drawing, the reference character K designates a vessel for.holding a pool of molten zinciferous lead to be refined, which may beheated by any conventional method, not shown in the drawing. Extendingacross the vessel K and resting upon the rim thereof, are two or moresteel beams W which support a unit comprising a motor H and a pump A forcirculating a stream of lead to be treated. Pump A'is suspended from themotor H and is preferably located near the bottom of the vessel K.

A reaction chamber B which may be supported over vessel K by channels Rrests upon beams W. A flanged end B' is provided on the reaction chamberand has secured thereto a head S for sealing the end thereof. Associatedwith reaction chamber B is an opening S in head S to provide an inletfor the chlorine gas, an inlet T near the top for introducing the impurelead, and an outlet L near the bottom for the withdrawal of the treatedlead and the products of reaction. If desired, opening T mayconveniently be placed at the top of the chamber, or inlet S may be atthe side near the top, and outlet L may be located at the bottom ofchamber B. A connecting pipe I connects the dischargeend of pump A to anozzle V projecting into reaction chamber B through opening T. A pipeline J connects inlet opening S to a source of supply of chlorine gas,not shown in the drawing.

A separating chamber C for separating the treated lead from the zincchloride may be supported over vessel K by beams W at a lower level thanreaction chamber B. The top of the separating chamber C may be flangedand a head C may be secured to it for the purpose of sealing the topthereof. An inlet opening N is provided near the bottom of chamber Cwhich may be connected by connecting line M to discharge opening L ofreaction chamber B. Directly in front and at a convenient distance frominlet opening N is a baffle O upwardly extending from the inside bottomof chamber C for the purpose of deflecting the incoming stream of moltenfluids upwardly. Inlet opening N may, however, be placed at a higherlevel in which case the baffle 0 may be dispensed with.

In connection with separating chamber C is also a siphon-like dischargesystem which may comprise an outlet opening Q at the side D of thechamber, an internal baille P for the purpose of preventing theoutflowing of the zinc chloride and an external baflle E to preventsplashing and to direct the flow of the refined lead from outlet Qdirectly to vessel K. Battle P, which may be cast as an integral part ofchamber C extending inwardly from' the top of opening Q to a point nearthe bottom of the chamber, forms with side D an internal closed ductwhich is open at the bottom and leads to opening Q. Outside ballle Eforms with wall D an external closed duct, which may be sealed at theupper end by plate E and which extends downwardly from opening Q bywhich it is connected to the aforementioned internal duct to a wideroutlet Z. The lower end of outlet Z may be made to extend below thesurface of molten lead in vessel K and, if desired,

ber C, outlet Q also may control the level of the molten fluids inreaction chamber B which is so placed in relation to chamber C as tomaintain the level above discharge opening L for the purpose ofpreventing escape of chlorine gas thereof. The level of the moltenfluids in chamber B may also be controlled by the height of baffle 0, ifit is found desirable to place outlet opening Q at a lower level.

In carrying the present invention into practice, the pump A is flrststarted and a stream of the lead to be-reflned is thereby made tocirculate for a few minutes through the apparatus in order to warm upreaction chamber B and to establish a level of molten lead up to outletQ of chamber C, thereby sealing discharge opening L of chamber B, forthe purpose of preventing escape of chlorine gas thereof. The rate ofcirculation of the lead is then adjusted to any desired value and thechlorine is turned on at a predetermined rate of flow which depends onthe amount of lead circulated and on the amount of zinc in the lead.

The treated lead and the zinc chloride resulting from the reactionbetween the chlorine gas and the zinc inthe lead flow out of reactionchamber B through outlet opening L and are led by connecting pipe M intoseparating chamber C through inlet opening N thereof. The separation ofthe lighter zinc chloride from the heavier treated lead in separatingchamber C is effected by gravity. In order to facilitate theirseparation the incoming stream of mixed fluids is upwardly deflected bybattle 0 and led to, or near the surface of the molten bath in chamberC, thereby the heavier treated lead sinks to a lower level and thelighter zinc chloride is left floating at the top. Two layers are thusformed in separatory chamber C, the upper layer consisting substantiallyof zinc chloride, and the lower layer of treated lead which isincreasingly free from zinc chloride at the lower levels thereof.Separating chamber C can remain full up to the level of outlet openingQ, but it is sufliciently large to' hold all the zinc chloride formed indezincing all the lead in kettle K. Flange P, moreover, is made toextend into the lower layer of the treated lead, thereby substantiallyentrapping the upper layer of zinc chloride at all times during therefining operation and allowing the discharging of treated lead onlysubstantially free from zinc chloride.

At the end of the refining process, the flow of chlorine and of the leadare stopped and valves F and G at the bottom of separating chamber C areopened to drain out the refined lead remaining in the chamber. The zincchloride is then drained through the same valve openings into separatecontainers.

The rate of flow of the molten lead and of chlorine gas into reactionchamber B may be adjusted for a higher speed of dezincing reaction thanit has heretofore been possible, because escape of chlorine from chamberB is substantially prevented by controlling the level of the moltenfluids above outlet opening thereof, as described more fullyhereinabove. Moreover, the rate of the reaction between the chlorine gasand the zinc in the lead need not be retarded so as to keep thetemperature of the lead bath below the temperature at which zincchloride begins to volatilize, or below about 750 F., because during theprocess the hot zinc chloride is kept in a closed chamber, whichpractically eliminates losses through volatilization and throughoxidation. Separating chamber C tends to somewhat reduce the temperatureof the treated lead which is returned to kettle K, thus preventingexcessive rising in temperature of the main body of molten lead inkettle K, such as was experienced in prior processes and requiredspecial cooling means to cool the bottom and sides of the kettle inorder to avoid excessive temperatures. 7

It is to be observed from the above description that the presentinvention provides an efficient and improved process for dezincing leadby means of chlorine in which the zinc chloride and the refined lead areobtained in two separate bodies; the zinc chloride substantially in amarketable form and the refined lead substantially free of zincchloride.

It is also to be seen that a considerable amount of delay and manuallabor are avoided, that losses of chlorine through volatilization ofzinc chloride are practically eliminated, and that the speed of thedezincing process can be carried at a faster rate than it has heretoforebeen possible.

It is to be understood that the hereinabove description of an apparatushas been given for illustrative purpose only and that many variationsand modifications may be resorted to without departing from the spiritof the invention. Thus, for example, separating chamber C may be substituted by an open chamber, or a centrifugal machine, or the like, bywhich the heavier lead may be centrifugally separated from the lighterzinc chloride.

Although in describing the present invention, the removal of zinc frommolten lead has been given as a specific example, it is to be observedthat other metallic impurities, whose heat of reaction with chlorine arehigher than that of lead, can also be removed by the same process as anyone skilled in the art will readily understand.

1. The improved method of refining molten zinciferous lead with chlorinegas which comprises treating a portion of zinc-bearing molten leadwithdrawn from a pool of molten zinci'ferous lead in a reaction chamberfor converting the zinc contaminating said lead into zinc chloride,withdrawing the treated lead containing zinc chloride to a separatorychamber for effecting separation of the zinc chloride from the treatedlead, and returning the treated lead substantially free from zincchloride to the pool of molten lead.

2. The improved method of refining molten zinciferous lead with chlorinegas which comprises establishing a pool of molten lead containing zinc,treating portions of the lead with chlorine gas in.a reaction chamberfor converting the zinc contaminating said lead into zinc chloride,effecting the separation of the zinc chloride from the treated leadoutside of the main pool of molten lead, and returning the treated leadsubstantially free from zinc chloride to said pool of molten lead.

3. The improved method of refining molten zinciferous lead with chlorinegas which comthe treated lead outside of the reaction chamber andoutsideof the main pool of molten lead, and

returning the treated lead substantiallyfree from zinc chloride to saidpool of molten lead.

- 4. The improved method of refining molten zinciferous lead withchlorine gas which com prises, establishing a pool of molten leadcontaining zinc, treating portions of the lead with chlorine gas in areaction chamber for converting the zinc contaminating said lead intozinc chloride, transferring the zinc chloride and the treated lead to aseparatory chamber for effecting separation of said zinc chloride fromsaid treated lead, and returning the treated lead substantially freefrom zinc chloride to the main pool of molten lead.

5. The improved method of refining molten zinciferous lead with chlorinegas which comprises establishing a pool of molten lead contain ing zinc,treating portions of the lead with chlorine gas in a reaction chamberfor converting the zinc contaminating said lead into zinc chloride,transferring the zinc chloride and the treated lead to a separatorychamber for effecting separation by gravity of said zinc chloride fromsaid treated lead, and returning the treated lead substantially freefrom zinc chloride to the main pool of molten lead.

6. The improved method of refining molten zinciferous lead with chlorinegas which comprises establishing a pool of molten lead containing zinc,treating portions of the lead with chlorine gas in a reaction chamberfor converting the zinc contaminating said lead into zinc chloride,transferring the zinc chloride and the treated lead to a separatorychamber, directing the flow of said zinc chloride and said treated leadto a point higher than the bottom of said separating chamber to promoteseparation by gravity thereof and to form an upper layer ofsubstantially only zinc chloride and a lower layer of substantially onlytreated lead, and returning the treated lead substantially free fromzinc chloride to the main pool of molten lead.

7. The improved method of refining molten zinciferous lead with chlorinegas which comprises establishing a pool of molten lead containing zinc,treating portions of the lead with chlorine gas in a reaction chamberfor converting the zinc contaminating said lead into zinc chloride,

conveying the treated lead containing zinc chloride from the reactionchamber to the bottom of the separatory chamber, upwardly deflecting theflow of said treated lead containing zinc chloride to promote separationby gravity thereof and to treated lead, and returning the treated leadsubstantially free from zinc chloride to the main pool of molten lead;

8. The; improved. method of refining molten zinciferous lead withchlorine gas which comprises establishing apool of molten leadcontaining zinc, treating portions of the lead with chlorine gas in areaction chamber for converting the zinc contaminating said lead intozinc chloride, conveying the treated lead containing zinc chloride fromthe reaction chamber to the bottom of the separatory chamber, upwardlydeflecting the fiow of said treated lead containing zinc chloride topromote separation by gravity thereof and to ing zinc, treating portionsof the lead with chlorine gas in a reaction chamber for converting thezinc contaminating said lead into zinc chloride, conveying the treatedlead containing zinc chloride from the reaction chamberto the bottom ofthe separatory chamber, upwardly deflecting the flow of said treatedlead containing zinc chloride to promote separation by gravity thereofto form an upper layer of substantially only zinc chloride and a lowerlevel of substantially only treated 20' lead, and returning the treatedlead substantially free from m'nc chloride to the main pool of moltenlead in substantially a continuous manner while preventing the outwardflow of the zinc chloride with the treated lead.

10. The improved method of refining molten zinciferous lead withchlorine gas which com prises treating a portion of zinc-bearing moltenlead withdrawn from a pool of molten zinciferous lead in a reactionchamber for converting the zinc contaminating said lead into zincchloride, withdrawing the treated lead containing zinc chloride to aseparatory chamber for efiecting separation of the zinc chloride fromthe treated lead, equalizing the levels of themolten products ofreaction in the reaction chamber and in the separatory chamber,controlling the level in said separatory chamber so that the level inthe reaction chamber is maintained above the discharge opening thereofto prevent escape of chlorine gas therefrom, and returning the treatedlead substantially free from zinc chloride to the pool of molten lead.

11. An improved apparatus for refining molten zinciferous lead withchlorine gas which comprises a vessel for holding a pool of molten leadcontaining zinc, a separate gas .chlorinating chamber connected to saidvessel for'treating por- I tions ofthe zinciferous lead with chlorinegas for converting the zinc contaminating the lead into zinc chloride,means for circulating molten zinciferous lead from said vessel to saidreaction chamber, means 'for introducing chlorine gas into the reactionchamber, a separate vessel connected with'said chlorinatlng chamber andwith said vessel for effecting the separation of zinc chloride fromtreated lead, means for transferthe reaction chamber to the separatoryvessel, and means for returning treated lead substaniially free fromzinc chloride to'said vessel. Y

13. An improved apparatus for refining molten zinciferous lead withchlorine gas which comprises a vessel for holding a pool of molten leading portions of the zinciferous lead with chlorine gas for convertingthe zinc contaminating the lead into zinc chloride, means forcirculating molten zinciferous lead from said vessel to said reactionchamber, means for introducing chlorine gas into the reaction chamber, aseparatory vessel for effecting the separation of zinc chloride fromtreated lead byv gravity, means for directing the flow of the treatedlead containing zinc chloride from the reaction chamber to a pointhigher than the bottom of the separatory vessel for promoting separationby gravity thereof and for forming an upper layer of substantially zincchloride and a lower level of substantially treated lead, and means forreturning treated lead substantially free from zinc chloride to saidvessel.

14. An improved apparatus for refining molten zinciferous lead withchlorine gas which comprises a vessel for holding a pool of molten leadcontaining zinc, a reaction chamber for treating portions of thezinciferous lead with chlorine gas for converting the zinc contaminatingthe lead into zinc chloride, means for circulating molten zinciferouslead from said vessel to said reaction 15. In an apparatus for refiningmolten zinc-' iferous lead with chlorine gas, that improvement whichcomprises a separating vessel for effecting the separation of zincchloride from treated lead, comprising a chamber having an inlet openingnear the or at the bottom and'an outlet opening, a vertical baflielocated adjacent of said inlet opening and extending upwardly fromthe-bottom of the chamber in an intermediate region to deflect upwardlythe flow of the incoming molten lead containing zinc chloride, aninternal closed duct leading to the outlet opening from a point near thebottom substantially for preventing the outward flow of the zincchloride, a closed duct downwardly extendingfrom the outlet opening toreturn the treated lead substantially free from zinc chloride.

16. An improved apparatus for refining molten zinciferous lead withchlorine gas which comprises a vessel for holding a pool of molten leadcontaining zinc, a separate gas chlorinating chamber connected to saidvessel for converting the zinc contaminating said lead into zincchloride, and aseparate vessel connected with said chlorinating chamberand with said vessel for eflecting aseparation of said zinc chloridefrom said treated lead having enough capacity to hold substantially allthe zinc chloride formed in refining substantially the entire pool ofmolten .lead. ring treated lead containing zinc chloride from 17. Animproved apparatus for refining molten zinciferous lead with chlorinegas which comprises a vessel for holding a pool of molten leadcontaining zinc, a reaction chamber for converting the .zinccontaminating said lead into zinc chloride, a separatory vessel foreffecting a separation of said zinc chloride from said treated leadhaving enough capacity to hold substantially all the zinc chlorideformed in refining substantially the entire pool of molten lead, andhaving an outlet opening for returning treated lead substantially freefrom zinc chloride which prises a vessel for holding a pool of moltenlead containing zinc, a reaction chamber for convertmg the zinccontaminating said lead into zinc chloride, a 'separatory vessel forefl'ecting a separation or said zinc chloride from said treated leadhaving enough capacity to hold substantially all the zinc chlorideformed in refining substantially the entire pool of molten lead, andhaving a vertical baflle located adjacent to the inlet opening 01' saidseparatory vessel which extends upwardly irom the bottom of the chamberto a level substantially higher than the outlet opening of said reactionchamber.

PAUL WEFELSCHEID.

